Recognize wide character literal

For now, L'' is equivalent to ''.

test/literal.c

@@ -95,6 +95,9 @@ int main() {
 of(char), \
          "sizeof(char)");
 
+  ASSERT(4, sizeof(L'\0'));
+  ASSERT(97, L'a');
+
   printf("OK\n");
   return 0;
 }

tokenize.c

@@ -432,6 +432,13 @@ Token *tokenize(File *file) {
       continue;
     }
 
+    // Wide character literal
+    if (startswith(p, "L'")) {
+      cur = read_char_literal(cur, p + 1);
+      p += cur->len + 1;
+      continue;
+    }
+
     // Identifier or keyword
     if (is_ident1(*p)) {
       char *q = p++;